There is known a white LED where an LED (Light Emitting Diode) generating blue light and a phosphor generating yellow fluorescence that are combined with each other thus generating white light. In white LEDs of this type, to realize high luminance, high reliability, and long lifetime, an emitting color conversion member where an inorganic phosphor is mixed into a glass is disclosed in Patent Literature 1 (JP2010-174246A). Compared with a white LED formed of a mixture of a yellow phosphor and a transparent resin, the white LED disclosed in Patent Literature 1 has an advantageous point that performance degradation of the white LED minimally diminishes due to deterioration of a resin.
There has been known a light source device and a projector which use a phosphor wheel where a phosphor is formed on a rotatable disk. The phosphor on the phosphor wheel is irradiated with excitation light such as blue light, and generated green fluorescence and yellow fluorescence are used as illumination light for a micro display of a liquid crystal panel or a DMD or the like. A light source device and a projector of this type can obtain fluorescence that has high luminance up to a certain level corresponding to the intensity of excitation light that irradiates a phosphor. Conventionally, a device where a fluorescent material which emits yellow color or the like is dispersed into a resin binder, and the mixture is applied and fixed to a substrate is, in fact, already being used. Patent Literature 2 (Japanese Patent No. 5530165) discloses a device where a plate-like inorganic phosphor is fixed on a substrate by adhesion or the like.
An inorganic phosphor exhibits desirable reliability with respect to irradiation of strong excitation light and hence, a projector which projects a bright image can be realized. Examples of an inorganic phosphor or phosphor ceramic include dispersing phosphor powder into a glass, a glass phosphor where emission center ions are added to a glass parent, a single crystal of a phosphor, a polycrystalline body of a phosphor or the like.
According to Patent Literature 2, a method of manufacturing such an inorganic phosphor includes a starting material mixing step, a molding step, a sintering step, and a processing step. For example, when Y3Al5O12:Ce3+ phosphor is used as a yellow phosphor, oxides of constituent elements of Y3Al5O12:Ce3+ phosphor such as a yttrium oxide, a cerium oxide, and alumina, and carbonate, nitrate, sulfate and the like which become oxides after sintering are used as starting materials. These materials are proportioned so as to satisfy a stoichiometric ratio, and are sufficiently dispersed and mixed with each other using water or an organic solvent by a wet ball mill.
Next, the mixture is molded into a predetermined shape. For a molding method, a uniaxial pressure method, a cold isostatic pressing method, a slip casting method, an injection molding method or the like can be used. The obtained molded body is burned at 1600 to 1800° C. With such processing, Y3Al5O12:Ce3+ phosphor ceramic can be obtained. The sintered body obtained as described above is polished so as to have a thickness of several tens to several hundreds of pin by an automatic polishing device or the like. Further, the sintered body is cut into a plate having a desired shape such as a circular shape, a quadrangular shape, a fan shape, or a ring shape by dicing or by scribing using a diamond cutter or a laser, and the sintered body obtained as described above is used. The above-mentioned technique is disclosed.
When thinking about manufacturing a phosphor wheel with ϕ30 or ϕ50, or greater than ϕ70 in large phosphor wheels, first, a cylindrical sintered body of a phosphor is produced corresponding to the outer shape of a substrate. Usually, a phosphor wheel is formed such that an inorganic phosphor plate having a toroidal shape or a C shape obtained by cutting away a portion from a toroidal shape is fixed on a circular substrate. Accordingly, to produce an inorganic phosphor plate having a toroidal shape, a cylindrical sintered body is sliced thus obtaining an inorganic phosphor plate. On the other hand, to produce an inorganic phosphor plate having a C shape, a cut-away portion is further formed on the sliced sintered body. Then, the plate-like inorganic phosphor is fixed to the substrate by adhesion or the like. That is, a cylindrical sintered body of a phosphor is prepared corresponding to the outer shape of the substrate. According to cases, arcuate sintered bodies may be obtained where an inorganic phosphor plate having a toroidal shape is split into three or four members.